This isn't very good but I think you can improve it. For starters, try going into more detail. Also try and introduce quotes and making longer chapters. Also, try doing what happened in the movie but give a bunch of good twists to make it more original.

As a small suggestion, maybe later when they're on the island, maybe put Alvin in a similar position Mater was in in Cars 2. Meaning where he feels bad about himself and like he's a fool or something.

o my gosh how can you think this is bad it super here are some ideas there not very good but here they go
IDEAS:
the chipmunks and the chipettes have a kind of sing off without dave knowing but when they were going back to the room something makes them slip off the boat and its to late when dave finds out luckily the chipmunks and chipettes get stranded on an island then alvin ''conforts'' brittany and somehow end up kissing eleanor gets almost attacked by some animal and since theodore was near helped her and you know they kiss and maybe jeanette hid from everyone and when she think shes alone starts crying eveyone was looking for her but simon finds her and they somehow kiss